A polyphenylene ether resin is a useful high polymeric material as engineering plastic because of its heat resistance, mechanical strength, and electrical characteristics. However, a polyphenylene ether resin is known to be inferior in solvent resistance, oil resistance, and molding properties as is common to noncrystalline resins.
In an attempt to compensate for poor molding properties of polyphenylene ether resin, it has been proposed to blend a polystyrene resin as disclosed in U.S. Pat. No. 3,383,435. This technique, however, does not bring about improvement on solvent resistance and oil resistance of polyphenylene ether resin.
It has also been proposed to compound a polyester resin into a polyphenylene ether resin thereby to improve molding properties, i.e., fluidity, of the polyphenylene ether resin as disclosed in Japanese Patent Publication No. 21664/76. As a result of studies, the present inventors have confirmed improvement of fluidity brought about by compounding the polyester resin. However, it has been turned out that compounding of the polyester resin in a proportion exceeding 20% by weight of the resulting composition results in great impairment of mechanical strength inherently possessed by the polyphenylene ether resin. This is considered ascribed to essential incompatibility between the polyphenylene ether resin and the polyester resin to cause significant phase separation as the amount of the polyester resin increases. In fact, the above-cited publication describes that the polymer blend of polyphenylene ether resin and polyester resin is "opaque" and has "a pearl-like tone", implying that the two resin components are not finely blended but nonuniformly dispersed involving phase separation.
Further, a polyester resin, when compounded into a polyphenylene ether resin, improves solvent resistance of the polyphenylene ether resin to an extent proportional to the amount compounded. Therefore, achievement of sufficient solvent resistance requires compounding of a large quantity of the polyester resin. As mentioned above, such compounding only produces a resin composition having reduced mechanical strength due to non-uniformity and phase separation.
In order to eliminate these disadvantages, it is necessary to improve compatibility between a polyphenylene ether resin and a polyester resin. To this effect, it has been suggested to incorporate a specific resin (phenoxy resin) into a composition of the polyphenylene ether resin and the polyester resin as disclosed in U.S. Pat. No. 4,614,773. According to this technique, the resulting composition has improved tensile strength but is found to have insufficient impact resistance, which would limit the use of the composition in the field requiring impact resistance, such as automobile exterior parts.